1. Field of the Invention
The present invention relates to a protocol control circuit for a data bus system. The protocol control circuit according to the present invention is applicable to a home bus system as one kind of data bus system.
2. Description of the Related Arts
Recently, a data communication system in a home has been developed in which data for the control of household electrical apparatuses in the home is communicated through a trunk data bus called a "home bus". Examples of known data communication systems using a home bus are illustrated in FIGS. 1A and 1B attached to this specification. As shown in FIG. 1A, a house is equipped with electrical units such as a broadcast receiving antenna, a security switch device, a smoke detector, a personal computer, an interphone, an air conditioner, a telephone set, a television receiver, an electric heated bath, a gas leakage detector, an electric cooking range, an electric lamp, a camera, an electric key device, a home controller, and the like, and each of these electrical units are interconnected by a home bus through a junction box for information transmission. A schematic diagram of the arrangement of the home bus system is shown in FIG. 2, in which a broadcast receiving antenna device, a tuner for television, a camera, a telephone set, an adapter for data communication, a device for hard copying information, a disk storage, and a work station are connected by a home bus. The work station includes a keyboard, a touch panel, a processor, a storage unit, and the like, and is connected to a video tape recorder, a display device, and a disk player.
In a data bus system such as a home bus system, however, a problem occurs in that, when it is desired to carry out transmission of data from this equipment connected to a data bus such as a home bus, if this equipment is receiving incoming data from the data bus, the desired transmission of data cannot be carried out until the equipment receives acknowledgement data from the data bus after receipt of the incoming data is completed.
This problem prevents an increase in the efficiency of transmission of acknowledgement data, and increases the burden on software of a central processor unit, and thus a data bus system having a satisfactory high operation efficiency has not yet been realized.